Neurotransmitter-gated membrane ion channels are among the most important target sites of alcohol action in the nervous system, although the manner in which alcohols modulate the function of these transmembrane proteins has not been established. The aim of this project is to investigate the actions of alcohols and related compounds on neurotransmitter-gated ion channels thought to be involved in producing the intoxicating effects of alcohols in nervous tissue. Previous studies have shown that the function of the N-methyl-D-aspartate (NMDA) receptor-channel, a type of receptor for the excitatory neurotransmitter glutamate, is inhibited by intoxicating concentrations of ethanol. Experiments were performed to identify the location of the site of alcohol action on the NMDA receptor in mammalian cells transfected with NR1/NR2B NMDA receptor subunits. Truncation of the intracellular C-terminal domain of the NR1 subunit did not alter ethanol sensitivity when combined with the NR2B subunit, but a similar truncation of the NR2B subunit slightly enhanced ethanol sensitivity of receptors formed from coexpression with either wild-type or C-terminally truncated NR1 subunits. 1-Pentanol applied externally potently inhibited NMDA receptors, but intracellular application of 1-pentanol did not alter NMDA receptor inhibition by externally applied ethanol or 1-pentanol. In addition, the amplitude of NMDA-activated current did not decrease during the time required for 1-pentanol to diffuse throughout the interior of the cell. Ethanol, even at high concentrations, did not inhibit NMDA receptors when bath-applied in cell-attached patches or when applied to the cytoplasmic face of inside-out membrane patches. These results appear to be best explained by an action of alcohols on the NMDA receptor-channel protein, at a site located in a domain exposed to, or only accessible from, the extracellular environment. Experiments in this unit have also been directed toward identification of the precise molecular site and mechanism of action of alcohols on the NMDA receptor, as well as the physiological regulation of glycine receptor-ion channels.